Sailboards typically include a buoyant board which is adapted to support a user on water, a mast which is connected to the board, a sail supported by the mast, and a boom which stretches the sail.
The sail is stretched between the mast and the aft end of the boom. With the boom securely mounted to the mast, the amount of outhaul position due to tension on the trailing edge of the sail determines the degree of curvature of the sail. Heretofore the user was able to set this curvature while on shore when "rigging" the sail by adjusting the tie-down tension on its trailing edge at the outer end of the boom. However, once the outhaul position was set there was no apparent means for changing this adjustment while the sailboard was underway and subject to variable wind and other sailing conditions.
The ability to modify the curvature of the sail can significantly affect the performance of the sailboard in the same way that the camber of an airplane wing and its angle of attack affects the wing lift. A "flatter" or low curvature sail gives optimum performance under high relative wing velocities, that is when the sailboard is tacking essentially upwind. Conversely, a high curvature sail produces optimum performance under low relative wind velocities, when the sailboard is moving more in a downwind direction. In addition, a "flatter" sail produces greater lift for steeper angles of attack relative to the wind. Thus, with the ability to flatten or reduce said curvature, a sailboard would be able to "point" further towards the wind direction and thereby enable the user to achieve optimum performance for all points of sail and for various wind speeds.